pythongh-101760: Improve the imaplib.IMAP4 example (python#101764)

Co-authored-by: Adam Turner <9087854+AA-Turner@users.noreply.github.com>

Doc/library/imaplib.rst

@@ -622,7 +622,7 @@ retrieves and prints all messages::
 
    import getpass, imaplib
 
-   M = imaplib.IMAP4()
+   M = imaplib.IMAP4(host='example.org')
    M.login(getpass.getuser(), getpass.getpass())
    M.select()
    typ, data = M.search(None, 'ALL')